Gas metal arc welding, commonly known as MIG (metal inert gas) welding, is a frequently used high deposition rate, semiautomatic welding process. A welding torch for MIG welding (e.g. described in U.S. Pat. No. 2,836,705) has a torch body that conducts electricity, receives a consumable welding wire, and has a diffuser that directs a shielding gas around a welding arc. During the welding process the electrical arc that extends between the welding wire and metal surfaces being welded is shielded within a gas flow.
It is well known in the welding industry that molten material or weld spatter generated by the welding arc is a major problem. During the welding process the spatter adheres to the nozzle. The spatter is made of the elements found in pieces being welded and the welding wire. The spatter is therefore prone to oxidization. Once spatter begins to attach to the nozzle, it continues to build up and oxidize and eventually restrict the flow of shielding gas to the weld. This results in a poor quality weld and eventually the destruction of the nozzle. If a robotic unit on a production line is doing the welding, this results in downtime for the whole production line.
A welding torch maintenance center (also called a reamer) for welding devices has been described in U.S. Pat. No. 4,583,257. In this embodiment, a base plate carries an axially advance able reaming head. A V-block and clamp head are aligned on the plate to locate and secure a robot-positioned welding torch nozzle in a vertical attitude. After clamping the nozzle in position, the reaming head is advanced into the nozzle bore to remove accumulated internal weld spatter. Typically, the reaming head is driven directly by a pressurized-air driven motor. The supply of the pressurized air is regulated by solenoid valves. The interface between the robot and the reamer is through the use of relay control between the reamer and other automation equipments. Other examples of reamers are described in U.S. Pat. Nos. 4,702,195; 4,834,280; 5,845,357; 6,023,045, 6,399,917, and Canadian patent CA2037489. Commercial versions of torch reamers can be found in http://www.binzel-abicor.com, http://www.toughgun.com, and http://www.thermadyne.com.
A disadvantage of the prior art reamers is that if the nozzle is not aligned concentrically with the cutter, because of the possibly asymmetrical nature of the spatter deposits on the walls of the nozzle, then the cutter removes part of the nozzle. This results in thermal distortion in the nozzle, leading to rapid welding torch failure.
Therefore, the existing welding torch nozzle cleaning stations have limited ability to ensure good quality nozzle cleaning.
In existing welding torch nozzle cleaning stations, the coordination of the sequence to place the torch nozzle on the reamer and the reaming process is ensured through the relay logics to control the signals between the robot and the reamer. Depending on the polarity of the power supply the relay logic can either control the supply of a positive pole (sourcing I/O) of the power supply or the 0 V return of the power supply (sinking I/O).
The pneumatic or relay logic of the existing reamers cannot automatically change from one configuration to the other; it is necessary to use adjust switches or jumpers by opening the enclosure and making adjustments inside the reamer.
To hold the nozzle, existing reamers have a stationary V-block and a pair of clamp, requiring manual adjustment and different V-blocks for different sizes of the nozzle.
Existing welding torch nozzle cleaning stations must position the torch nozzle by ‘trial and error’ procedures because they do not provide a means for programming the position at the point of use without additional equipment.
In the area of fault management and diagnostics the existing welding torch nozzle cleaning stations have very limited capabilities. They do not provide an indication that the entire reaming process has been completed successfully, in case of a failed operation they do not provide an error signal to the robot because of the lack of diagnostic capability and they do not have the capability to automatically retry if a problem (i.e. a stall) occurs during the reaming process.
Existing reamers do not have the capability to monitor or regulate the speed of the air-driven reaming motor, and to adjust the solenoids by changing the average amount of current drawn from the robot power supply.
Furthermore, current welding torch nozzle cleaning stations are not capable to communicate with other automation equipment on a communication network. Setup procedures and data acquisition may assist personnel in various activities required for plant management from various equipment communicating on a network. Existing welding torch nozzle cleaning stations may be equipped with an anti-spatter spray mechanism. This mechanism may be actuated synchronous with nozzle reaming or on its own. The anti-spatter fluid is atomized and sprayed into the nozzle in order to deter further spatter from adhering to the inside bore of the nozzle. A portion of the spray may inadvertently spray outside of the nozzle and into the atmosphere. When this portion of over spray falls and mixes with spatter cleaned out of the nozzle from the reaming process it creates a sticky tar on the supporting platform, which is difficult to clean.
Existing anti-spatter spray mechanisms do not monitor and are not capable of informing the operator when to refill the fluid reservoir.
The length of consumable welding wire sticking out from the end of the contact tip inside the nozzle is not always a consistent length. It is desirable to cut this wire to a predetermined length. Existing welding torch nozzle cleaning stations may be equipped with a wire cutter. The wire cutter may be stand alone or integrated with the reaming device. In the latter case, the start signal for the wire cutter is the same as the start signal for the reamer. The torch is positioned differently for each process, but the start signal will actuate both operations (reaming and wire cutting). The “finished” signal to the robot is not active until entire reaming process has been completed.
Existing welding torch nozzle cleaning stations check the positional accuracy of the end of the wire (tool center point) by moving the torch to a taught point such that the tip of the wire is at the vertex of a tapered cone so that the accuracy may be visually checked. Another mechanism for feeding back a positive verification of the end of the wire is a limit switch. The feedback device is stand-alone and a separate signal must be accommodated for it.
Existing nozzle cleaning stations and wire cutters do not provide a means of bypassing any sensors installed on the unit.
Existing nozzle cleaning stations do not provide a means to trial run the reaming operation.
Existing nozzle cleaning stations do not provide a way to cool the nozzle.
Existing nozzle cleaning stations may be operated by electrical signals or proximity signals mounted at or near the operative mechanism (reaming header, sprayer, wire cutter). The proximity signals activate the operative mechanism immediately; the power supply (air/electrical) must be disconnected in order to teach a proper position with the robot without actuating the mechanism.